<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style type="text/css">
			div{
				width: 100px;
				height: 100px;
			}
			div:first-child{
				background-color: yellow;
				 position: absolute;/* 让出文档空间，后续元素会自动向上 */
			}
			div:nth-child(2){
				background-color: blue;
				 z-index: 999;
				 position: relative; /* 如果没有特殊定位，偏移量和堆叠顺序属性无效 */
				 left: 50px;
				 top: 50px;
			}
		</style>
	</head>
	<body>
		<div></div>
		<div></div>
	</body>
</html>
